A new method is proposed to provide ventilatory support and to promote mucus clearance for infants suffering from respiratory insufficiency. The trunk and lower body of an infant is placed in an airtight chamber equipped with a neck-hole so that his head is exposed to either room air or a special head-box. The chamber pressure is oscillated rapidly about a mean pressure which may be subatmospheric. The negative pressure should distend his airways; the rapid oscillations will generate high-frequency shallow breaths, enabling him to engage in gas exchange and possibly also enhancing his mucus clearance. This method avoids the necessity of tracheal intubation, may reduce the risks of pulmonary air leaks and other forms of barotrauma, and is expected to produce less cardiovascular disturbances than the conventional mechanical ventilator. To assess the feasibility of this concept as well as to understand the physiological responses of different animals to rapid bodily oscillation, a number of parameters will be examined in four groups of animals, i.e., normal and surfactant-deficient adult rabbits as well as normal and surfactant-deficient newborn piglets. Three ventilatory states will be studied in most of the experiments proposed: spontaneous breathing, spontaneous breathing with superimposed high-frequency body-surface oscillation, and high-frequency body-surface oscillation alone. The physiological parameters to be examined are: a) gas exchange, including blood gas tensions, physiological dead space and possible gas transport mechanisms; b) cardiovascular function, including cardiac output, systemic vascular resistance, pulmonary vascular resistance and other hemodynamic responses to rapid intrapleural pressure variation; c) stability of intracranial pressure; d) respiratory mechanics, including lung compliance, dynamic compliance, lung and chest wall impedances and upper airway resistance; e) mucus production and clearance rates; and f) body heat loss, including the cardiopulmonary responses to moderate hypothermia. Adjunct to this main theme, the possibility of using low-amplitude high-frequency perithoracic compression as a form of cardiac assist will be explored, and a physical model and theoretical study aimed at gaining analytical knowledge about body heat loss will also be made.